The invention relates to a braking system for motor cycles equipped at the rear with a group comprising a spring and shock-absorber, the system being of the kind wherein a hydraulic master cylinder, usually pedal-actuated supplies a rear brake and a front brake, and wherein a pressure-regulating valve comprising a calibrating spring limits the maximum pressure on the rear brake to a predetermined value depending on the compression of the calibrating spring.
In the prior art, the pressure-regulating spring, which is usually secured to the motorcycle chassis, has a fixed calibration, i.e. the calibrating spring is calibrated so as to limit the maximum pressure on the rear brake to a predetermined fixed value.
The fixed value is determined in accordance with the maximum load on the motorcycle i.e. when it is carrying two persons weighing 75 kg each and 20 kg of baggage. It ensures optimum braking under the aforementioned maximum-load conditions.
The aforementioned system has a disadvantage in that when the motor cycle does not carry the maximum load, e.g. when it carries only a minimum load, i.e. the driver alone the rear braking is too sharp and abrupt.
A second disadvantage of the prior-art system, which occurs even under the maximum load conditions for which the system has been specially calibrated, is that, during braking, the load is transferred from the back wheel to the front wheel of the motorcycle as a result of inertia this produces varying load conditions on the back wheel, more particularly below the maximum load, so that the rear braking as before is too sharp and abrupt.
It has been suggested that the pressure-regulating valve should be provided with a manual control for varying the compression of the calibrating spring in accordance with the load conditions. This suggestion would obviate the first disadvantage but is impracticable in view of safety requirements, since, if the driver ever forgets to perform the manual operation for varying the compression of the calibrating spring, e.g., when a passenger gets onto his motorcycle the rear braking will be insufficient in that the calibration will accidentally have been left at the optimum value for the driver alone.
A second suggested solution, which would obviate both the first and the second aforementioned disadvantage, is likewise impracticable. According to the second solution, the compression of the calibrating spring is controlled by moving the rear suspension of the motorcycle relative to the chassis, by mechanically connecting the suspension to the free end of the calibrating spring of the pressure-regulating valve, which is secured to the chassis, so that when the suspension approaches the chassis there is an increase in the compression of the spring and vice versa.
This second solution is impracticable since a lever is disposed in a known manner between the chassis and the rear suspension on the spring and shock-absorber assembly of motor cycles. The lever is actuated by the driver so as to vary the position of the rear suspension in dependence on the load. As a result of the aforementioned means, the rear suspension is moved into a position relative to the chassis which is practically unaffected by variations in the load conditions. The aforementioned second solution is impracticable because the position of the rear suspension is carefully regulated in accordance with the load conditions.
The object of the invention is to provide a motor-cycle brake system which obviates the disadvantages of the existing systems and guarantees optimum rear braking under all load conditions on the back wheel, due either to variations in the loads carried by the motorcycle or to variations in load occurring during braking when the load is transferred from the back wheel to the front wheel by inertia.